Various abbreviations that appear in the specification and/or in the drawing figures are defined as below:                BS Base Station        CN Core Network        Device-to-Device D2D        eNB evolved Node B        E-UTRA Evolved Universal Terrestrial Radio Access        GW Gateway        MME Mobility Management Entity        ProSe Proximity based Service        UE User Equipment        
The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present disclosure but provided by the present disclosure. Some such contributions of the present disclosure may be specifically pointed out below, while other such contributions of the present disclosure will be apparent from their context.
With the rapid developments of an LTE system, a high-speed data service via low power nodes (e.g., a small cell BS) becomes increasingly important to suit the requirements of wireless communication users. It is known that the small cell BS, which is generally deployed to be closer to UEs than a macro BS in some certain areas, such as at hotspots, is capable of providing a relatively high speed data service. Therefore, how to provide ProSe communication either via direct D2D communication, or locally routed by a BS (or an eNB) without CN involved to achieve a high speed data rate under a wireless communication system, e.g., the LTE system, has become a hot topic in the 3GPP.